1. Field of the Invention:
This invention pertains to the tempering of glass using gaseous jets of a cooling fluid which usually consists of air.
2. Description of the Related Art
It is known that, for obtaining mark-free tempering of glass sheets by blowing a cooling gas thereon, said glass sheets and blowing elements should be shifted with respect to each other.
In the case of horizontal tempering, i.e., when the glass sheets are arranged horizontally, the blowing elements are generally stationary, while the glass sheets move; in the case of vertical tempering, there can be an oscillation of both blowing elements and glass sheets.
This relative shift of glass and blowing elements is mentioned especially in French Patent. Nos. 2,547,575; 1,133,039; 1,158,738; 1,476,785.
Under such conditions, it is possible to temper slightly bulged glass sheets, but when glass volumes which are highly convex and/or which have multiple curvatures in different directions, such as half-spheres, are involved, any relative movement of the glass sheets and the blowing elements with respect to each other is impossible, except by moving the glass sheets and the blowing elements far apart. But, in that case, the necessary blowing pressures become too high and the space between the glass and the blowing means fluctuates too much for the tempering to be homogeneous.
Moreover, any shift, either of glass or of blowing elements, can take place only with a relatively low frequency, whereas the quality of the tempering increases with the frequency of the relative shift of glass and blowing elements.
It has already been proposed, in an attempt to resolve the problem of the frequency of the relative shift of glass and blowing elements, to lighten the blowing elements that are made to oscillate and to instead set only the blowing nozzles into oscillation (French Patent No. 1,550,733). But there still remains a movement of mechanical elements which limits the frequency of the oscillations. Moreover, the impossibility of the relative movement of glass and of blowing elements with respect to one another for highly bulged glass sheets and those having multiple curvatures has not been resolved.
It was also proposed in French Patent No. 83-4514 to vary, during the cooling of the glass for the purpose of tempering it, either the position of the cooling zones or their active intensity, or both, by causing two or more jets, whose flow was altered in relation to time, to interact as they issue from their respective nozzles. This would seem to be a possible solution for the problems presented by the movements of the blowing elements and/or the oscillations of glass sheets opposite these means; however, this is not the case.
Indeed, the multiplication of the number of nozzles in order to obtain an interaction of the jets issuing therefrom creates an obstacle which hinders the escape of tempering air and which thus significantly reduces its efficiency. In addition, this technique requires special blowing elements, tuyere in this case, and significant flows and pressures for each of these nozzles, resulting in relatively high equipment and operating costs.